gh-133259: Show path to python.sh script on successful build

[mdboom]

This is a slightly different solution than @brettcannon suggested. At least on my machine, my CPython checkout is pretty deep, so it's nice to just show the path relative to the checkout.

• Issue: Make the python.sh script more discoverable #133259

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 RHEL8 LTO 3.x (tier-2) has failed when building commit c141340.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/338/builds/8688) and take a look at the build logs.
4. Check if the failure is related to this commit (c141340) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/338/builds/8688

Failed tests:

• test_frame

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 5, done.        
remote: Counting objects: 100% (1/1)        
remote: Counting objects: 100% (1/1), done.        
remote: Total 5 (delta 0), reused 0 (delta 0), pack-reused 4 (from 1)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to 'c14134020f44575635e11e4552cefcfd8cdbe22f'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at c14134020f4 gh-133259: Show path to python.sh script on successful build (#133268)
Switched to and reset branch 'main'

make: *** [Makefile:2453: buildbottest] Error 2